Communication methods, communication device station and access point

ABSTRACT

The present invention provides a new trigger frame dedicated to NDP feedback procedure. This NDP feedback trigger frame comprises a specific field allowing stations (non-AP nodes) receiving this trigger frame to identify it as being a dedicated NDP feedback trigger frame. Thanks to this specific field, a receiving station knows that a NDP feedback procedure has started and that a NDP feedback is expected by the access point. The present invention also provides for communication methods using this NDP feedback trigger frame, communication device station and access point configured to implement these methods, and also a wireless communication network comprising such devices.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/474,521, filed Jun. 27, 2019, titled “Communication Methods,Communication Device Station and Access Point”, and issued as U.S. Pat.No. 11,197,275 on Dec. 7, 2021, which is a National Phase application ofPCT Application No. PCT/EP2018/050279, filed on Jan. 5, 2018 and titled“Communication Methods, Communication Device Station and Access Point.”This application claims the benefit under 35 U.S.C. 119(a)-(d) of UnitedKingdom Patent Application Nos. GB 1700429.2, filed on Jan. 10, 2017.The above cited patent applications are incorporated herein by referencein their entirety.

FIELD OF THE INVENTION

The present invention relates generally to communication networks andmore specifically to communication networks offering channel accesses tonodes through contention and providing secondary accesses to the nodesto sub-channels (or Resource Units) splitting a transmission opportunityTXOP granted to an access point, in order to transmit data.

The invention finds application in wireless communication networks, inparticular in 802.11ax networks offering, to the nodes, an access to an802.11ax composite channel and/or to Resource Units forming for instancean 802.11ax composite channel granted to the access point and allowingUplink communication to be performed.

BACKGROUND OF THE INVENTION

The IEEE 802.11 MAC standard defines the way Wireless local areanetworks (WLANs) must work at the physical and medium access control(MAC) level. Typically, the 802.11 MAC (Medium Access Control) operatingmode implements the well-known Distributed Coordination Function (DCF)which relies on a contention based mechanism based on the so-called“Carrier Sense Multiple Access with Collision Avoidance” (CSMA/CA)technique.

The 802.11 medium access protocol standard or operating mode is mainlydirected to the management of communication stations waiting for thewireless medium to become idle so as to try to access to the wirelessmedium.

The network operating mode defined by the IEEE 802.11ac standardprovides very high throughput (VHT) by, among other means, moving fromthe 2.4 GHz band which is deemed to be highly susceptible tointerference to the 5 GHz band, thereby allowing for wider frequencycontiguous channels of 80 MHz to be used, two of which may optionally becombined to get a 160 MHz channel as operating band of the wirelessnetwork.

The 802.11ac standard also tweaks control frames such as theRequest-To-Send (RTS) and Clear-To-Send (CTS) frames to allow forcomposite channels of varying and predefined bandwidths of 20, 40 or 80MHz, the composite channels being made of one or more communicationchannels that are contiguous within the operating band. The 160 MHzcomposite channel is possible by the combination of two 80 MHz compositechannels within the 160 MHz operating band. The control frames specifythe channel width (bandwidth) for the targeted composite channel.

A composite channel therefore consists of a primary channel on which agiven node performs EDCA backoff procedure to access the medium, and ofat least one secondary channel, of for example 20 MHz each.

EDCA (Enhanced Distributed Channel Access) defines traffic categoriesand four corresponding access categories that make it possible to handledifferently high-priority traffic compared to low-priority traffic.

Implementation of EDCA in the nodes can be made using a plurality oftraffic queues (known as “Access Categories”) for serving data trafficat different priorities, each traffic queue being associated with arespective queue backoff value. The queue backoff value is computed fromrespective queue contention parameters, e.g. EDCA parameters, and isused to contend for access to a communication channel in order totransmit data stored in the traffic queue.

Conventional EDCA parameters include CWmin, CWmax and AIFSN for eachtraffic queue, wherein CWmin and CWmax are the lower and higherboundaries of a selection range from which an EDCA contention window CWis selected for a given traffic queue. AIFSN stands for ArbitrationInter-Frame Space Number, and defines the number of time slots (usually9 μs), additional to a DIFS interval (the total defining the AIFSperiod) the node must sense the medium as idle before decrementing thequeue backoff value associated with the traffic queue considered.

The EDCA parameters may be defined in a beacon frame sent by a specificnode in the network to broadcast network information.

The contention windows CW and the queue backoff values are EDCAvariables.

Conventional EDCA backoff procedure consists for the node in selecting aqueue backoff value for a traffic queue from the respective contentionwindow CW, and then to decrement it upon sensing the medium as idleafter the AIFS period. Once the backoff value reaches zero, the node isallowed to access the medium.

The EDCA queue backoff values or counters thus play two roles. First,they drive the nodes in efficiently accessing the medium, by reducingrisks of collisions; second, they offer management of quality ofservice, QoS, by mirroring the aging of the data contained in thetraffic queue (the more aged the data, the lower the backoff value) andthus providing different priorities to the traffic queues throughdifferent values of the EDCA parameters (especially the AIFSN parameterthat delays the start of the decrementing of the EDCA queue backoffvalues).

Thanks to the EDCA backoff procedure, the node can thus access thecommunication network using contention type access mechanism based onthe queue contention parameters, typically based on the computed queuebackoff counter or value.

The primary channel is used by the communication nodes to sense whetheror not the channel is idle, and the primary channel can be extendedusing the secondary channel or channels to form a composite channel. Theprimary channel can also be used alone.

Given a tree breakdown of the operating band into elementary 20 MHzchannels, some secondary channels are named tertiary or quaternarychannels.

In 802.11ac, all the transmissions, and thus the possible compositechannels, include the primary channel. This is because the nodes performfull Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) andNetwork Allocation Vector (NAV) tracking on the primary channel only.The other channels are assigned as secondary channels, on which thenodes have only capability of CCA (clear channel assessment), i.e.detection of an idle or busy state/status of said secondary channel.

An issue with the use of composite channels as defined in the 802.11n or802.11ac (or 802.11ax) standards is that the nodes compliant with a useof composite channels (i.e. 802.11n-compliant node (already known as HTnodes standing for High Throughput nodes), 802.11ac-compliant nodes(already known as VHT nodes standing Very High Throughput nodes) and802.11ax-compliant nodes (already known as HE nodes standing HighEfficiency nodes)) have to co-exist with legacy nodes not able to usecomposite channels but relying only on conventional 20 MHz channels(i.e. non-HT nodes compliant only with for instance 802.11a/b/g).

To cope with this issue, the 802.11n and 802.11ac and 802.11ax standardsprovide the possibility to duplicate control frames (e.g. RTS/CTS orCTS-to-Self or ACK frames to acknowledge correct or erroneous receptionof the sent data) over each 20 MHz channel in an 802.11a legacy format(called as “non-HT”) to establish a protection of the requested TXOPover the whole composite channel.

This is for any legacy 802.11a node that uses any of the 20 MHz channelinvolved in the composite channel to be aware of on-going communicationson the 20 MHz channel. As a result, the legacy node is prevented frominitiating a new transmission until the end of the current compositechannel TXOP granted to an 802.11n/ac/ax node.

MHz non-HT control frames to be sent simultaneously on both the primaryand secondary channels forming the used composite channel.

This approach has been widened for 802.11ac to allow duplication overthe channels forming an 80 MHz or 160 MHz composite channel. In theremainder of the present document, the “duplicated non-HTFrame” or“duplicated non-HT control frame” or “duplicated control frame” meansthat the node device duplicates the conventional or “non-HT”transmission of a given control frame over secondary 20 MHz channel(s)of the (40 MHz, 80 MHz or 160 MHz) operating band.

In practice, to request a composite channel (equal to or greater than 40MHz) for a new TXOP, an 802.11n/ac node performs an EDCA backoffprocedure in the primary 20 MHz channel as mentioned above. In parallel,it performs a channel sensing mechanism, such as aClear-Channel-Assessment (CCA) signal detection, on the secondarychannels to detect the secondary channel or channels that are idle(channel state/status is “idle”) during a PIFS interval before the startof the new TXOP (i.e. before any queue backoff counter expires).

More recently, Institute of Electrical and Electronics Engineers (IEEE)officially approved the 802.11ax task group, as the successor of802.11ac. The primary goal of the 802.11ax task group consists inseeking for an improvement in data speed to wireless communicatingdevices used in dense deployment scenarios.

Recent developments in the 802.11ax standard sought to optimize usage ofthe composite channel by multiple nodes in a wireless network having anaccess point (AP). Indeed, typical contents have important amount ofdata, for instance relating to high-definition audio-visual real-timeand interactive content. Furthermore, it is well-known that theperformance of the CSMA/CA protocol used in the IEEE 802.11 standarddeteriorates rapidly as the number of nodes and the amount of trafficincrease, i.e. in dense WLAN scenarios.

In this context, multi-user (MU) transmission has been considered toallow multiple simultaneous transmissions to/from different users inboth downlink (DL) and uplink (UL) directions from/to the AP and duringa transmission opportunity granted to the AP. In the uplink, multi-usertransmissions can be used to mitigate the collision probability byallowing multiple non-AP stations or non-AP nodes to simultaneouslytransmit. In the following document, we refer to non-AP nodes as“stations” or STA, by opposition to AP nodes.

To actually perform such multi-user transmission, it has been proposedto split a granted communication channel into sub-channels, alsoreferred to as resource units (RUs), that are shared in the frequencydomain by multiple users (non-AP stations/nodes), based for instance onOrthogonal Frequency Division Multiple Access (OFDMA) technique. Each RUmay be defined by a number of tones, the 80 MHz channel containing up to996 usable tones.

OFDMA is a multi-user variation of OFDM which has emerged as a new keytechnology to improve efficiency in advanced infrastructure-basedwireless networks. It combines OFDM on the physical layer with FrequencyDivision Multiple Access (FDMA) on the MAC layer, allowing differentsubcarriers to be assigned to different stations/nodes in order toincrease concurrency. Adjacent sub-carriers often experience similarchannel conditions and are thus grouped to sub-channels: an OFDMAsub-channel or RU is thus a set of sub-carriers.

As currently envisaged, the granularity of such OFDMA sub-channels isfiner than the original 20 MHz channel band. Typically, a 2 MHz or 5 MHzsub-channel may be contemplated as a minimum width, therefore definingfor instance 9 sub-channels or resource units within a single 20 MHzchannel.

The multi-user feature of OFDMA allows the AP to assign or offerdifferent RUs to different non-AP stations/nodes in order to increasecompetition. This may help to reduce contention and collisions inside802.11 networks.

The 802.11ax standard defines a Trigger frame (TF) that is sent by theAP to the 802.11ax non-AP nodes (i.e. to the 802.11ax stations) totrigger Multi-User uplink communications, i.e. solicit the transmissionof uplink (UL) Multi-User (OFDMA) PPDU from multiple nodes. The TFdefines the resource units as provided by the AP to the nodes. Inresponse, the nodes transmit UL MU (OFDMA) PPDU as immediate responsesto the Trigger frame. All transmitters can send data at the same time,but using disjoint sets of RUs (i.e. of frequencies in the OFDMAscheme), resulting in transmissions with less interference.

The width of the targeted composite channel is signalled in the TFframe, meaning that the 20, 40, 80 or 160 MHz value is added. The TFframe is sent over the primary 20 MHz channel and duplicated(replicated) on each other 20 MHz channels forming the targetedcomposite channel, if appropriate. As described above for theduplication of control frames, it is expected that every nearby legacynode (non-802.11ax nodes) receiving the TF on its primary channel, thensets its NAV to the value specified in the TF. This prevents theselegacy nodes from accessing the channels of the targeted compositechannel during the TXOP.

A resource unit RU can be reserved for a specific node, in which casethe AP indicates, in the TF, the node to which the RU is reserved. SuchRU is called Scheduled RU. The indicated node does not need to performcontention on accessing a scheduled RU reserved to it.

In order to better improve the efficiency of the system with regards tounmanaged traffic to the AP (for example, uplink management frames fromassociated nodes, unassociated nodes intending to reach an AP, or simplyunmanaged data traffic), resource units may be proposed by the AP to the802.11ax nodes through contention-based access. In other words, theresource unit RU can be randomly accessed by more than one node. Such RUis called Random RU and is indicated as such in the TF. Random RUs mayserve as a basis for contention between nodes willing to access thecommunication medium for sending data.

As readily apparent from the above, the Multi User Uplink medium accessscheme (or RU access scheme) allows the number of collisions generatedby simultaneous medium access attempts to be reduced, while alsoreducing the overhead due to the medium access since the medium accesscost is shared between several nodes.

In a dense environment such as in a network compliant with the 802.11axstandard, bandwidth consumption rate and all extra overheads areimportant matters. In order to optimize bandwidth consumption, theaccess point (AP) aims at controlling the access to the medium bymanaging grant of RUs to the non-AP stations (STA). To optimize resourceunits (RUs) allocation, the AP preferably has a global view of the nodesrequirements as precisely as possible. A problem is that the AP does notknow when new bursts arrive in STAs buffer (small packets, or firstpackets of a longer burst of data).

The 802.11ax standard provides a mechanism for polling all STAs of the802.11ax cell to get the status of data queues. This mechanism (called“BSR (for Buffer Status Report) mechanism”) consists in sending adedicated BSR trigger frame soliciting each node to answer with a bufferstatus report packet as described in the 802.11ax standard (see Draft1.0—Clause 27.5.2.5).

One single node is solicited at a time. This may be problematic in hugeenvironments (typically in a 802.11ax cell driving a high number of IOTdevices for Internet Of Things) as the AP has to send multiple BSRtrigger frames to solicit all STAs of the 802.11ax cell, even if only afew number of STAs have some remaining data packets to be transmitted inits queues. Thus, bandwidth is consumed for no real impact for futuretransmissions since all STAs are polled while only few responses matter.

Moreover, the trigger frame uses the same medium access scheme as asingle data packet. It means that some other transmissions can beperformed by other STAs between BSR trigger frames. As a consequence,the result of the BSR mechanism may be obsolete when all STAs arefinally polled about their future data transmissions.

To address these bandwidth and obsolescence issues, the clause 27.5.2.7of the draft 1.0 of the 802.11ax standard proposes an additionalmechanism called NDP (Null Data Packet) feedback report procedure. TheNDP packet is a single packet with no data payload and thus allowsbuilding very short responses. In sounding protocols, it allows adaptingbeamforming antenna for multiple STAs in an 802.11 cell in costeffective manner.

The NDP feedback procedure has a low and stable latency compared topossibly high and unpredictable latency with conventional CSMA-CAmechanisms when used in dense environments.

A problem is that no implementation for the NDP feedback procedure isproposed in the 802.11 ax standard. There is thus a need to provide acomplete mechanism defining the NDP feedback mechanism.

SUMMARY OF INVENTION

The present invention has been devised to address one or more of theforegoing concerns.

In this context, according to a first aspect of the invention, there isprovided a communication method in a wireless communication networkcomprising an access point (AP) and a plurality of stations (non-AP),the method comprising, at the access point:

-   -   accessing a communication channel to send a trigger frame        reserving a transmission opportunity on the communication        channel and defining resource units, RUs, forming the        communication channel for the stations to transmit data to the        access point;    -   wherein the trigger frame comprises a first field allowing        stations receiving it to identify the trigger frame as being        dedicated to initiate collection of feedbacks from stations of        the plurality during the reserved transmission opportunity.

Typically, this first field is a “Trigger Type” field having a valuespecific to the NDP feedback procedure as mentioned below.

The claimed invention thus provides an implementation of a NDP feedbackmechanism using a specific NDP feedback trigger frame enabling toretrieve short feedbacks from a very high number of communication nodesin a dense 802.11 environment.

Thanks to the specific NDP feedback trigger frame, the access point isbetter aware of the state of the nodes, i.e. has a better global andmore accurate (in real time) view of the nodes requirements (e.g.resource requests) and abilities (e.g. low/high level of battery)without this causing overloads or excessive latencies due to very shortNDP feedback responses.

Advantageously, a better control of the access to the medium by bettermanaging grant of RUs to the nodes (non-AP stations) is achieved. Hence,bandwidth occupancy is better optimized compared to the prior art.

Correspondingly, there is provided an access point (AP) in a wirelesscommunication network also comprising a plurality of stations (non-AP),the access point comprising at least one microprocessor configured forcarrying out the following step:

-   -   accessing a communication channel to send a trigger frame        reserving a transmission opportunity on the communication        channel and defining resource units, RUs, forming the        communication channel for the stations to transmit data to the        access point;    -   wherein the trigger frame comprises a first field allowing        stations receiving it to identify the trigger frame as being        dedicated to initiate collection of feedbacks from stations of        the plurality during the reserved transmission opportunity.

The access point has the same advantages as the method defined above.

Optional features of the invention are further defined in the dependentappended claims. Some of these features are explained here below withreference to a method, while they can be transposed into device featuresdedicated to an access point according to the invention.

According to embodiments, the trigger frame comprises a second fieldindicating a type of feedbacks to be collected from the stations.

Advantageously, any type requesting a few bits answer only can be askedin the NDP feedback trigger frame. In this way, the initial usage(resource feedbacks) of the NDP feedback procedure may be advantageouslyextended to various types. For instance, the type may relate to thebattery level of the mobile stations or the temperature level of IOT(Internet Of Things) devices.

This second field is typically a “Service Info” field as described belowand the type is typically indicated in the “Question” subfield of this“Service Info” field as described below.

According to embodiments, the feedback response is received by theaccess point in a packet with no data payload.

According to embodiments, the type calls for resource requests from thestations. It avoids reserving and loosing resource units for stationsthat have no data to transmit.

According to embodiments, the type is about the status of at least onecomponent of the station.

Many IOT devices can be polled for avoiding multiple medium accessesfrom IOT devices when they have very short data packets to transmit.Finally the bandwidth consumption is optimized.

According to embodiments, the type is a closed-ended question.

Such a closed-ended question allows analyzing the received NDP feedbackpacket using a single energy detection mechanism. The access point canthus optimize the time to analyze all the received NDP feedback packets.

According to embodiments, the trigger frame comprises informationindicating a group of stations to be polled by the access point.

According to embodiments, the second field comprises a subfieldindicating a group of stations to be polled by the access point. Thissubfield is typically a “ClientID” field as described below.

It allows selecting a group of stations without extra overhead. Whenstations are divided into multiple groups, it allows minimizing the sizeof the “Map Info” field mentioned below or extending the “Map Info”field mentioned below when its size is limited.

According to embodiments, the trigger frame comprises a third fieldspecifying the position at which a feedback responsive to the triggerframe should be sent. This third field is typically a “Map Info” fieldas described below.

This third field may comprise a feedback map specifying, for eachselected station, the position at which a feedback responsive to thetrigger frame should be sent.

A polled station can thus determine the exact position where to send itsNDP feedback packet without any collision with the other polledstations.

According to embodiments, the third field comprises at least one stationidentifier and at least one RU number.

According to embodiments, the third field also comprises a time positionand/or a spatial position.

The number of polled stations for one NDP feedback trigger frame is thusincreased and the extra overhead is minimized.

According to embodiments, the method comprises the following steps:

-   -   selecting a service;    -   selecting at least one station to be polled about the selected        service; building the trigger frame based on the selected        service and an identifier of the at least one station to be        polled.

According to embodiments, the method also comprises building a feedbackmap for the selected station(s), the feedback map specifying, for eachselected station, the position at which a feedback responsive to thetrigger frame should be sent, and building the trigger frame is alsobased on the feedback map.

According to embodiments, the method also comprises gathering theselected stations having MIMO capabilities in a first group and theselected stations without MIMO capabilities in a second group, andbuilding a feedback map is based on the first and the second group.

According to embodiments, the method also comprises the following steps:

-   -   receiving at least one feedback response to the trigger frame;    -   analyzing the received feedback response(s).

According to embodiments, analyzing uses a single energy detectionmechanism.

According to a second aspect of the invention, there is provided acommunication method in a wireless communication network comprising anaccess point (AP) and a plurality of stations (non-AP),

-   -   the method comprising, at a station    -   receiving a trigger frame reserving a transmission opportunity        on the communication channel and defining resource units, RUs,        forming the communication channel for the stations to transmit        data to the access point;    -   wherein the trigger frame comprises a first field allowing the        station to identify the trigger frame as being dedicated to        initiate collection of feedbacks from stations of the plurality        during the reserved transmission opportunity.

Thus, when receiving a trigger frame, the station knows that it is a NDPfeedback trigger frame. The station thus knows that a NDP feedbackprocess is being performed on the communication channel and that a NDPfeedback procedure has started and that a NDP feedback is expected bythe access point.

Correspondingly, there is provided communication device station in awireless communication network comprising an access point (AP) and aplurality of stations (non-AP), the communication device comprising atleast one microprocessor configured for carrying out the following step:

-   -   receiving a trigger frame reserving a transmission opportunity        on the communication channel and defining resource units, RUs,        forming the communication channel for the stations to transmit        data to the access point;    -   wherein the trigger frame comprises a first field allowing the        station to identify the trigger frame as being dedicated to        initiate collection of feedbacks from stations of the plurality        during the reserved transmission opportunity; and    -   wherein the trigger frame further comprises a second field        indicating a type of feedbacks to be collected from the        stations.

The communication device station has the same advantages as the methoddefined above.

Optional features of the invention are further defined in the dependentappended claims. Some of these features are explained here below withreference to a method, while they can be transposed into device featuresdedicated to any communication device station according to theinvention.

According to embodiments, the method also comprises the following steps:

-   -   determining whether the station is targeted by the received        trigger frame; and if so    -   building a feedback response to the received trigger frame; and    -   sending the feedback response to the access point in the        transmission opportunity reserved by the access point.

According to embodiments, the feedback response is sent in a packet withno data payload, i.e. a null data packet (NDP).

According to embodiments, the method also comprises identifying, basedon the received trigger frame, a position at which a feedback responseto it should be sent, and sending the feedback response to the accesspoint is done at the identified position.

This position is typically indicated in a feedback map of a “Map Info”field as described below. This feedback map specifies, for each stationtargeted in the trigger frame, the position at which a feedbackresponsive to the trigger frame should be sent.

Hence, collisions between NDP feedback packets are avoided.

According to embodiments, the method also comprises the following steps:

-   -   retrieving, based on the second field in the received trigger        frame, a type of feedbacks to be collected from the stations;        and    -   determining the response to the type;    -   and the feedback response is built based on the determined        response.

The type is typically indicated in the “Question” subfield of a “ServiceInfo” field as described below.

Advantageously, since a wide variety of types may be asked the polledstation is not limited to send resource feedbacks but can send otherkinds of feedbacks depending on the type asked. For instance, the polledstation may provide feedbacks about its battery level or its temperaturelevel.

According to embodiments, the type is a closed-ended question.

Such a closed-ended question is easy to answer for the communicationdevice station and allows the access point to analyze the received NDPfeedback packet using a single energy detection mechanism.

According to a third aspect of the invention, there is a providedwireless communication network comprising a plurality of communicationdevice stations as aforementioned and an access point as aforementioned.

According to a fourth aspect of the invention, there is provided adedicated Null Data Packet (NDP) feedback trigger frame designed to besent by an access point (AP) of a wireless communication networkcomprising a plurality of stations (non-AP), the NDP feedback triggerframe comprising a second field indicating a type of feedbacks to becollected from the stations.

This trigger frame dedicated to the NDP feedback procedure comprises aspecific field allowing stations (non-AP nodes) receiving this triggerframe to identify it as being a dedicated NDP feedback trigger frame.Thanks to this specific field, a receiving station knows that a NDPfeedback procedure has started and that a NDP feedback is expected bythe access point.

The type is typically indicated in the “Question” subfield of a “ServiceInfo” field as described below.

Advantageously, any type requesting a few bits answer only can be askedin the NDP feedback trigger frame. In this way, the initial usage(resource feedbacks) of the NDP feedback procedure may be advantageouslyextended to various questions. For instance, the type may relate to thebattery level of the mobile stations or the temperature level of IOT(Internet Of Things) devices.

According to embodiments, the type calls for resource requests fromstations able to receive the NDP feedback trigger frame.

It avoids reserving and loosing resource units for stations that have nodata to transmit.

According to embodiments, the type is about the status of at least onecomponent of a station able to receive the NDP feedback trigger frame.

According to embodiments, the type is a closed-ended question.

Such a closed-ended question is easy to answer for the communicationdevice station and allows the access point to analyze the received NDPfeedback packet using a single energy detection mechanism. Furthermore,the access point can thus optimize the time to analyze all the receivedNDP feedback packets.

According to embodiments, the trigger frame comprises informationindicating the group of stations to be polled.

According to embodiments, the second field comprises a subfieldindicating a group of stations to be polled. This subfield is typicallya “ClientlD” field as described below.

It allows selecting a group of stations without extra overhead. Whenstations are divided into multiple groups, it allows minimizing the sizeof the “Map Info” field mentioned below or extending the “Map Info”field mentioned below when its size is limited.

According to embodiments, the trigger frame comprises a third fieldspecifying the position at which a feedback responsive to the NDPfeedback trigger frame should be sent.

This third field is typically a “Map Info” field as described below.

It may comprise a feedback map specifying, for each polled station, theposition at which a feedback responsive to the trigger frame should besent.

A given polled station can thus determine the exact position where tosend its NDP feedback packet without any collision with the other polledstations.

According to embodiments, the third field comprises at least one stationidentifier and at least one RU number.

According to embodiments, the third field also comprises a time positionand/or a spatial position.

The number of polled stations for one NDP feedback trigger frame is thusincreased and the extra overhead is minimized.

Another aspect of the invention relates to a non-transitorycomputer-readable medium storing a program which, when executed by amicroprocessor or computer system in a device, causes the device toperform any method as defined above.

The non-transitory computer-readable medium may have features andadvantages that are analogous to those set out above and below inrelation to the methods and devices.

Other aspects of the invention relates to method, substantially asherein described with reference to, and as shown in, FIGS. 9 and 10 ofthe accompanying drawings.

At least parts of the methods according to the invention may be computerimplemented. Accordingly, the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit”, “module” or “system”. Furthermore,the present invention may take the form of a computer program productembodied in any tangible medium of expression having computer usableprogram code embodied in the medium.

Since the present invention can be implemented in software, the presentinvention can be embodied as computer readable code for provision to aprogrammable apparatus on any suitable carrier medium. A tangiblecarrier medium may comprise a storage medium such as a hard disk drive,a magnetic tape device or a solid state memory device and the like. Atransient carrier medium may include a signal such as an electricalsignal, an electronic signal, an optical signal, an acoustic signal, amagnetic signal or an electromagnetic signal, e.g. a microwave or RFsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent tothose skilled in the art upon examination of the drawings and detaileddescription. Embodiments of the invention will now be described, by wayof example only, and with reference to the following drawings.

FIG. 1 illustrates a typical wireless communication system in whichembodiments of the invention may be implemented;

FIG. 2 illustrates 802.11ac channel allocation that supports channelbandwidths of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;

FIG. 3 illustrates an example of 802.11ax uplink OFDMA transmissionscheme, wherein the AP issues a trigger frame for reserving atransmission opportunity of OFDMA sub-channels (resource units) on an 80MHz channel as known in the art;

FIG. 4 shows a schematic representation a communication device orstation according to embodiments of the present invention;

FIG. 5 shows a block diagram schematically illustrating the architectureof a wireless communication device according to embodiments of thepresent invention;

FIG. 6 illustrates the structure of a NDP Feedback trigger frameaccording to embodiments of the present invention;

FIG. 7 illustrates the structure of a NDP Feedback packet as known inthe art;

FIG. 8 illustrates a NDP feedback procedure using a dedicated triggerframe according to embodiments of the present invention;

FIG. 9 illustrates, using a flowchart, steps of a communication methodperformed by an access point (AP) according to embodiments of thepresent invention when the access point generates and transmits a NDPfeedback Trigger frame;

FIG. 10 illustrates, using a flowchart, steps of a communication methodperformed by a station (non-AP node) STA, according to embodiments ofthe invention, when the node receives a NDP feedback Trigger frame.

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limitingexemplary embodiments and by reference to the figures.

FIG. 1 illustrates a communication system in which several communicationnodes (or stations) 101, 102, 103, 104, 105, 106 and 107 exchange dataframes over a radio transmission channel 100 of a wireless local areanetwork (WLAN), under the management of a central station, or accesspoint (AP) 110 with which the nodes have registered. The radiotransmission channel 100 is defined by an operating frequency bandconstituted by a single channel or a plurality of channels forming acomposite channel.

Access to the shared radio medium to send data frames is based on theCSMA/CA technique, for sensing the carrier and avoiding collision byseparating concurrent transmissions in space and time.

To meet the ever-increasing demand for faster wireless networks tosupport bandwidth-intensive applications, 802.11ac is targeting largerbandwidth transmission through multi-channel operations.

FIG. 2 illustrates 802.11ac channel allocation that supports channelbandwidths of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art.

IEEE 802.11ac introduces support of a restricted number of predefinedsubsets of 20 MHz channels to form the sole predefined composite channelconfigurations that are available for reservation by any 802.11ac nodeon the wireless network to transmit data.

The predefined subsets are shown in the figure and correspond to 20 MHz,40 MHz, 80 MHz, and 160 MHz channel bandwidths, compared to only 20 MHzand 40 MHz supported by 802.11n. Indeed, the 20 MHz component channels300-1 to 300-8 are concatenated to form wider communication compositechannels.

In the 802.11ac standard, the channels of each predefined 40 MHz, 80 MHzor 160 MHz subset are contiguous within the operating frequency band,i.e. no hole (missing channel) in the composite channel as ordered inthe operating frequency band is allowed.

The 160 MHz channel bandwidth is composed of two 80 MHz channels thatmay or may not be frequency contiguous. The 80 MHz and 40 MHz channelsare respectively composed of two frequency-adjacent or contiguous 40 MHzand 20 MHz channels, respectively. However the present invention mayhave embodiments with either composition of the channel bandwidth, i.e.including only contiguous channels or formed of non-contiguous channelswithin the operating band.

A node is granted a TXOP through the enhanced distributed channel access(EDCA) mechanism on the “primary channel” (200-3). Indeed, for eachcomposite channel having a bandwidth, 802.11ac designates one channel as“primary” meaning that it is used for contending for access to thecomposite channel. The primary 20 MHz channel is common to all nodes(STAs) belonging to the same basic set, i.e. managed by or registeredwith the same local Access Point (AP).

However, to make sure that no other legacy node (i.e. not belonging tothe same 802.11 network or cell) uses the secondary channels, it isprovided that the control frames (e.g. RTS frame/CTS frame) reservingthe composite channel are duplicated over each 20 MHz channel of suchcomposite channel.

As addressed earlier, the IEEE 802.11ac standard enables up to four, oreven eight, 20 MHz channels to be bound. Because of the limited numberof channels (19 in the 5 GHz band in Europe), channel saturation becomesproblematic. Indeed, in densely populated areas, the 5 GHz band willsurely tend to saturate even with a 20 or 40 MHz bandwidth usage perWireless-LAN cell.

Developments in the 802.11ax standard seek to enhance efficiency andusage of the wireless channel for dense environments.

In this perspective, one may consider multi-user (MU) transmissionfeatures, allowing multiple simultaneous transmissions to/from differentusers in both downlink (DL) and uplink (UL) directions with a main node,usually an AP. In the uplink, multi-user transmissions can be used tomitigate the collision probability by allowing multiple nodes tosimultaneously transmit to the AP.

As illustrated with reference to FIG. 3 , to actually perform suchmulti-user transmission, it has been proposed to split a granted 20 MHzchannel into sub-channels (elementary sub-channels), also referred to assub-carriers or resource units (RUs), that are shared in the frequencydomain by multiple users, based for instance on Orthogonal FrequencyDivision Multiple Access (OFDMA) technique.

In the given example, each 20 MHz channel 300-1, 300-2, 300-3 or 300-4is sub-divided in the frequency domain into four sub-channels or RUs310, typically of size 5 MHz.

Of course the number of RUs splitting a 20 MHz channel may be differentfrom four. For instance, between two to nine RUs may be provided (thuseach having a size between 10 MHz and about 2 MHz).

The multi-user feature of OFDMA allows, a node, usually an access point,AP, to assign different RUs to different nodes in order to increasecompetition. This may help to reduce contention and collisions inside802.11 networks.

Contrary to MU downlink OFDMA wherein the AP can directly send multipledata to multiple nodes (supported by specific indications inside thePLCP header), a trigger mechanism has been adopted for the AP to triggerMU uplink communications from various nodes.

To support a MU uplink transmission (during a TxOP pre-empted by theAP), the 802.11ax AP has to provide signalling information for bothlegacy nodes (non802.11ax nodes) to set their NAV and for 802.11ax nodesto determine the Resource Units allocation.

In the following description, the term legacy refers to non-802.11axnodes, meaning 802.11 nodes of previous technologies that do not supportOFDMA communications.

As shown in the example of FIG. 3 , the AP sends a trigger frame (TF)330 to the targeted 802.11ax nodes. The bandwidth or width of thetargeted composite channel is signalled in the TF frame, meaning thatthe 20, 40, 80 or 160 MHz value is signalled. The TF frame is sent overthe primary 20 MHz channel and duplicated (replicated) on each other 20MHz channels forming the targeted composite channel. As described abovefor the duplication of control frames, it is expected that every nearbylegacy node (non-HT or 802.11ac nodes) receiving the TF frame (or aduplicate thereof) on its primary channel, then sets its NAV to thevalue specified in the TF frame. This prevents these legacy nodes fromaccessing the channels of the targeted composite channel during theTXOP.

Based on an AP's decision, the trigger frame TF may define a pluralityof resource units (RUs) 310. These RUs can be scheduled RU or “RandomRUs”.

Scheduled RUs may be reserved by the AP for certain nodes in which caseno contention for accessing such RUs is needed for these nodes. Such RUsand their corresponding scheduled nodes are indicated in the triggerframe. For instance, a node identifier, such as the Association ID (AID)assigned to each node upon registration, is added, in the TF frame, inassociation with each Scheduled RU in order to explicitly indicate thenode that is allowed to use each Scheduled RU.

Random RUs can be randomly accessed by the nodes of the network. Inother words, Random RUs designated or allocated by the AP in the TF mayserve as basis for contention between nodes willing to access thecommunication medium for sending data. A collision occurs when two ormore nodes attempt to transmit at the same time over the same RU. An AIDequal to 0 may be used to identify random RUs.

The trigger frame containing only random RUs is referred to as a triggerframe for random access (TF-R). A TF-R may be emitted by the AP to allowmultiple nodes to perform MU UL (Multi-User UpLink) random access toobtain an RU for their UL transmissions.

The AP can assign only one scheduled RU per non-AP STA and random RU canbe accessed by non-AP STA that are not polled by scheduled RUs in thesame TF. This may help to reduce contention and collisions inside 802.11networks.

Once the nodes have used the RUs to transmit data to the AP, the APresponds with an acknowledgment ACK (not show in the figure) toacknowledge the data on each RU, making it possible for each node toknow when its data transmission is successful (reception of the ACK) ornot (no ACK after expiry of a time-out).

Document IEEE 802.11-15/1105 provides an exemplary random allocationprocedure that may be used by the nodes to access the Random RUsindicated in the TF. This random allocation procedure, referred to as RUcontention scheme, is managed by a dedicated RU access module separatefrom the above-mentioned channel access module and is configured tomanage access to at least one resource unit provided by another node(usually the AP) within a transmission opportunity granted to the othernode on the communication channel, in order to transmit data storedlocally over an accessed resource unit. Preferably, the RU access moduleincludes an RU backoff engine separate from the queue backoff engines,which uses RU contention parameters, including a computed RU backoffvalue, to contend for access to the random RUs.

In other words, the RU contention scheme is based on a new backoffcounter, referred to as the OFDMA or RU backoff counter/value (or OBO),inside the 802.11ax nodes for allowing a dedicated contention whenaccessing a random RU to send data.

Each node STA1 to STAn is a transmitting node with regards to receivingAP, and as a consequence, each node has an active RU backoff engineseparate from the queue backoff engines, for computing an RU backoffvalue (OBO) to be used to contend for access to at least one randomresource unit splitting a transmission opportunity granted on thecommunication channel, in order to transmit data stored in eithertraffic queue AC.

The random allocation procedure in this document comprises, for a nodeof a plurality of nodes having an active RU backoff value OBO, a firststep of determining from the trigger frame the random sub-channels orRUs of the communication medium available for contention, a second stepof verifying if the value of the active RU backoff value OBO local tothe considered node is not greater than a number ofdetected-as-available random RUs, and then, in the case of a successfulverification, a third step of randomly selecting a random RU among thedetected-as-available random RUs for sending data. In case the secondstep is not verified, a fourth step (instead of the third) is performedin order to decrement the RU backoff value OBO by the number ofdetected-as-available RUs.

As shown in the figure, some Resource Units may not be used (310 u)because no node with an RU backoff value OBO less than the number ofavailable random RUs has randomly selected one of these random RUs,whereas some other have collided (as example 310 c) because two of thesenodes have randomly selected the same RU.

The MU Uplink (UL) medium access scheme, including both scheduled RUsand random RUs, proves to be very efficient compared to conventionalEDCA access scheme. This is because the number of collisions generatedby simultaneous medium access attempts and the overhead due to themedium access are both reduced.

FIG. 4 schematically illustrates a communication device 400 of the radionetwork 100, configured to implement at least one embodiment of thepresent invention. The communication device 400 may preferably be adevice such as a microcomputer, a workstation or a light portabledevice. The communication device 400 comprises a communication bus 413to which there are preferably connected:

-   -   a central processing unit 411, such as a microprocessor, denoted        CPU;    -   a read only memory 407, denoted ROM, for storing computer        programs for implementing the invention;    -   a random access memory 412, denoted RAM, for storing the        executable code of methods according to embodiments of the        invention as well as the registers adapted to record variables        and parameters necessary for implementing methods according to        embodiments of the invention; and    -   at least one communication interface 402 connected to the radio        communication network 100 over which digital data packets or        frames or control frames are transmitted, for example a wireless        communication network according to the 802.11ax protocol. The        frames are written from a FIFO sending memory in RAM 412 to the        network interface for transmission or are read from the network        interface for reception and writing into a FIFO receiving memory        in RAM 412 under the control of a software application running        in the CPU 411.

Optionally, the communication device 400 may also include the followingcomponents:

-   -   a data storage means 404 such as a hard disk, for storing        computer programs for implementing methods according to one or        more embodiments of the invention;    -   a disk drive 405 for a disk 406, the disk drive being adapted to        read data from the disk 406 or to write data onto said disk;    -   a screen 409 for displaying decoded data and/or serving as a        graphical interface with the user, by means of a keyboard 410 or        any other pointing means.

The communication device 400 may be optionally connected to variousperipherals, such as for example a digital camera 408, each beingconnected to an input/output card (not shown) so as to supply data tothe communication device 400.

Preferably the communication bus provides communication andinteroperability between the various elements included in thecommunication device 400 or connected to it. The representation of thebus is not limiting and in particular the central processing unit isoperable to communicate instructions to any element of the communicationdevice 400 directly or by means of another element of the communicationdevice 400.

The disk 406 may optionally be replaced by any information medium suchas for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, aUSB key or a memory card and, in general terms, by an informationstorage means that can be read by a microcomputer or by amicroprocessor, integrated or not into the apparatus, possibly removableand adapted to store one or more programs whose execution enables amethod according to the invention to be implemented.

The executable code may optionally be stored either in read only memory407, on the hard disk 404 or on a removable digital medium such as forexample a disk 406 as described previously. According to an optionalvariant, the executable code of the programs can be received by means ofthe communication network 403, via the interface 402, in order to bestored in one of the storage means of the communication device 400, suchas the hard disk 404, before being executed.

The central processing unit 411 is preferably adapted to control anddirect the execution of the instructions or portions of software code ofthe program or programs according to the invention, which instructionsare stored in one of the aforementioned storage means. On powering up,the program or programs that are stored in a non-volatile memory, forexample on the hard disk 404 or in the read only memory 407, aretransferred into the random access memory 412, which then contains theexecutable code of the program or programs, as well as registers forstoring the 5 variables and parameters necessary for implementing theinvention.

In a preferred embodiment, the apparatus is a programmable apparatuswhich uses software to implement the invention. However, alternatively,the present invention may be implemented in hardware (for example, inthe form of an Application Specific Integrated Circuit or ASIC).

FIG. 5 is a block diagram schematically illustrating the architecture ofa communication device or node 400, in particular one of nodes 100-107,adapted to carry out, at least partially, the invention. As illustrated,node 400 comprises an application layer block 501, a MAC layer block502, and a physical (PHY) layer block 503.

The PHY layer block 503 (here an 802.11 standardized PHY layer) has thetask of formatting frames, modulating frames on or demodulating framesfrom any 20 MHz channel or the composite channel, and thus sending orreceiving frames over the radio medium used 100. The frames may be802.11 frames, for instance medium access trigger frames TF 430 todefine resource units in a granted transmission opportunity, MAC dataand management frames based on a 20 MHz width to interact with legacy802.11 stations, as well as of MAC data frames of OFDMA type havingsmaller width than 20 MHz legacy (typically 2 or 5 MHz) to/from thatradio medium.

The MAC layer block or controller 502 preferably comprises a MAC 802.11layer 504 implementing conventional 802.11ax MAC operations, and anadditional block 505 for carrying out, at least partially, theinvention. The MAC layer block 502 may optionally be implemented insoftware, which software is loaded into RAM 512 and executed by CPU 511.

Preferably, an additional block, referred to NDP Feedback Managementmodule 505 for managing the NDP feedback procedure, implements the partof the invention that regards node 400, i.e. transmitting operations fora source node, receiving operations for a receiving node.

On top of the figure, application layer block 501 runs an applicationthat generates and receives data packets, for example data packets of avideo stream. Application layer block 501 represents all the stacklayers above MAC layer according to ISO standardization.

FIG. 6 illustrates the structure of a NDP Feedback trigger frame 600according to embodiments of the present invention.

Embodiments of the present invention provide a trigger frame dedicatedto the NDP feedback procedure. It comprises a specific field allowingstations (non-AP nodes) receiving this trigger frame to identify it asbeing a dedicated NDP feedback trigger frame. Thanks to this specificfield, a receiving station knows that a NDP feedback procedure hasstarted and that a NDP feedback is expected by the access point.

Hence, the NDP feedback trigger frame 600 is an additional trigger framethat solicits and allocates resources for Multi-User UpLinktransmissions after a SIFS (Short Inter Frame Space) duration for allpolled stations. The trigger frame comprises information required by theresponding station to send a trigger-based PPDU as mentioned hereafterin the description with reference to FIG. 7 .

The NDP feedback trigger frame 600 is a control type frame with astandardized “Frame Control” field and a standardized “Duration” field(802.11ax standard—Draft 1.0—Clause 28.3.16). The “(RA)” field of thetrigger frame 600 comprises the broadcast address. The “TA” field valuecomprises the address of the access point transmitting the triggerframe.

The “Common Info” field 610 is compliant with the corresponding fielddescribed in the 802.11 ax standard (Draft 1.0—Clause 9.3.1.23.1) but,according to the present invention, the “Trigger Type” subfield 620 andthe “Trigger Dependent Common Info” subfield 630 differ from thecorresponding subfields of the 802.11ax standard.

According to embodiments, the “Trigger Type” subfield 620 comprises avalue specifying that the trigger frame is a dedicated NDP feedbacktrigger frame. Since in draft 1.0 of the 802.11ax standard, the values 0to 6 are already taken for other trigger frame type, it is proposed toreserve a different value, for instance 7. Obviously, other values thatare not already used for existing trigger frames may be used. Thanks tothis new value reserved for the new dedicated NDP feedback trigger frame600, a receiving station can identify the trigger frame as being a NDPfeedback trigger frame, thereby triggering the NDP feedback mechanism.

According to embodiments, the “Trigger Dependent Common Info” subfield630, which usually provides information depending on the trigger frametype, comprises a “Service Info” subfield 640 that may further comprisea “Question” subfield 641 and a “Group ID” subfield 642.

According to embodiments, the “Question” subfield 641 indicates aquestion (request) for which the access point requires a feedbackresponse. This question is preferably a closed-ended question. Forinstance, the closed-ended question may be “do you have data totransmit?” or “do you have enough battery to transmit?” or again “isyour temperature higher than the setpoint temperature?”.

Therefore, while the NDP feedback procedure as initially drafted in the802.11ax standard is intended to be used to retrieve resources feedbacksfrom a high number of stations, embodiments of the present inventionallow extending it to the monitoring of the status of multiple sensorsof the stations.

Hence, the implementation of the NDP feedback procedure proposed by thepresent invention allows any question requesting a few bits answer only,to be asked in the NDP feedback trigger frame 600. In this way, theinitial usage of the NDP feedback procedure may be advantageouslyextended to various questions.

According to embodiments, the “GroupID” subfield 642 indicates a groupof stations that are polled by the AP. To make it simple, a defaultvalue of the GroupID field is defined for the case where all stations ofthe 802.11 cell are concerned by the NDP feedback trigger frame 600.

Also, a dedicated value can be defined for instance for polling only asubset of stations such as IOT devices. This allows the number offeedback responses to the NDP feedback trigger frame 600 to be limited,thereby saving bandwidth.

The NDP feedback trigger frame 600 also comprises a “User Info” field650 that indicates the position at which the feedback response isexpected by the AP. This is because upon the NDP feedback trigger framereception, a Multi-User UpLink OFDMA transmission is initiated and sucha transmission is performed over a communication channel which isdivided into resource units (RU). The “User Info” field 650 thuscomprises a Map Info field 660 which defines the position at which thefeedback response is expected to be sent by the polled stations in theMulti-User UpLink OFDMA transmission. It should be noted that the term“position” may not refer only to the RU number but can have severaldimensions, for instance frequency, time and/or space. Thus, in someembodiments, the position may be tridimensional (frequency, time andspace).

For instance, this position may be defined by the following subfields:

-   -   the “RU Allocation” subfield 670 that indicates the RU number        used by the NDP feedback packet (i.e. NDP feedback response) of        the station identified by the AID subfield. The RU Allocation        subfield is typically 8 bits in length;    -   the “AID” subfield 671 that carries the least significant 12        bits of the AID of the station polled by the AP;    -   the optional “Spatial Position” subfield 672 that specifies the        spatial stream number used by the NDP feedback packet of the        station identified by the AID subfield;    -   the optional “Time Position” subfield (673) that specifies the        position in the time domain inside the RU used by the NDP        feedback packet of the station identified by the AID subfield.

As mentioned, the position can be characterized only by the “RUAllocation” field 670 specifying the RU to be used by the polled stationwith the AID in the “AID” subfield 671 to send the NDP feedback packet(i.e. NDP feedback response).

It should be noted that when the polled station targeted by the AIDindicated in the “AID” subfield 671 does not support transmission withmultiple spatial streams (i.e. MIMO technology), the “Spatial Position”subfield 672 of the “Map Info” field 660 is set to 1,

FIG. 7 illustrates the structure of a NDP feedback packet, i.e. a NDPfeedback response, as known in the art.

As mentioned before, the NDP packet is a single packet with no datapayload. This packet is a binary response of the polled station to atrigger frame sent by the access point.

This packet simply uses the PHY preamble to send a binary feedback tothe access point. The PHY preamble contains all standard fields and thesame PHY preamble as the data packets (such as trigger-based PPDUpacket). This preamble is robust. The format is the same as the PHYpreamble of the HE trigger-based PPDU packet that is identical to the HESU PPDU format for the L-STF, L-LTF, L-SIG, RLSIG, HE-SIG-A fields. Theformat of the HE SU PPDU packet is described in the clause 28.3.4 of thedraft 1.0 of the 802.11ax standard.

FIG. 8 illustrates a NDP feedback procedure using a dedicated triggerframe according to embodiments of the present invention.

To poll a high number of stations in an efficient manner, the accesspoint sends a NDP feedback trigger frame as described with reference toFIG. 6 . In this example, the NDP feedback trigger frame (802) is sentin a 20 MHz primary channel (800). But in another embodiment, thetrigger frame 802 can be sent through an extended channel such as 40MHz, 80 MHz or 160 MHz to extend the number of polled stations.

The NDP feedback trigger frame 802 is sent through the conventionalaccess categories using the standardized EDCA medium access mechanism.As described in the draft 1.0 of the 802.11ax standard, there is noparticular transmission priority for the trigger frame.

According to the present invention, the NDP feedback trigger frame 802comprises a “Service Info” subfield (not shown) that indicates thetargeted group of stations and defines a question to answer for thesestations. This targeted group may comprise all the stations of the cellor only a subpart of them, for instance having a specific functionality(e.g. IOT devices).

Also, the NDP feedback trigger frame 802 comprises a “Map Info” subfield(not shown) that defines a position at which the feedback response (i.e.the NDP feedback packet) is expected to be sent by each polled station.

By sending this trigger frame 802, the access point reserves atransmission opportunity 801 (TXOP) divided in multiple RUs 810 (RU 0),811 (RU 1), 812 (RU 2) and 813 (RU 3).

Upon the reception of the NDP feedback trigger frame 802, the stationanalyses the “Map Info” field and the “Service Info” field to determinewhether it belongs to the group of stations polled by the access point.

If this is the case, after a SIFS duration 803, the station sends a NDPFeedback packet 820 as described with reference to FIG. 7 , at theposition retrieved from the “Map Info” field of the received NDPfeedback trigger frame.

It should be noted that each RU can contain one or more NDP Feedbackpackets spread in time and/or spatial domain, notably when the positionis defined in these additional dimensions.

FIG. 9 illustrates, using a flowchart, steps of a communication methodperformed by an access point (AP) according to embodiments of thepresent invention when the access point generates and transmits a NDPfeedback trigger frame.

At step 900, the AP receives a request to send a new NDP feedbacktrigger frame. This request may be from the Application layer (501 inFIG. 5 ) or from the 30 MAC 802.11 layer (504 in FIG. 5 ). Such arequest may be sent periodically or the sending of the request may betriggered by a specific event.

For illustration purposes, the Application Layer may be an applicationfor controlling the temperature of a building. It may thus request thestatus of stations for a specific temperature level to take a decisionabout the heating system.

At step 910, the AP selects the appropriate kind of feedback to get,i.e. the question to ask in the “Service Info” field of the NDP feedbacktrigger frame.

At step 920, the stations to be polled are selected. For instance, allstations attached to the AP may be polled. This may be done by settingthe “GroupID” subfield of the NDP feedback trigger frame to a defaultvalue. In a variant, only part of the stations may be selected to bepolled. In this case, a dedicated value may be indicated in the“GroupID” subfield for this purpose.

At optional step 930, the stations selected at step 920 are separatedinto two groups: the selected stations having MIMO capabilities aregathered in a first group and the selected stations without MIMOcapabilities are gathered in a second group.

At step 940, the AP builds a NDP feedback map defining, for eachselected station, a position at which the feedback response (i.e. theNDP feedback packet) is expected to be sent by each polled station. ThisNDP feedback map will be specified in the “Map Info” field of the NDPfeedback trigger frame.

The optional step 930 allows simplifying the building of the NDPfeedback map at step 940. In particular, the “Spatial Position” subfieldof the “Map Info” field for these stations (without MIMO capabilities)may be set to 1. Then, it may be decided that all the selected stationswithout MIMO capabilities have to send their NDP feedback response (NDPpacket) on a different RU than stations having MIMO capabilities.

At step 950, the AP finally builds the NDP feedback trigger frame.

According to embodiments, the AP inserts a specific value in the“Trigger Type” field (620 in FIG. 6 ) for identifying the trigger frameas a NDP feedback trigger frame. This allows receiving stations to knowthat a NDP feedback process is being performed on the communicationchannel.

The NDP feedback trigger frame is then sent at step 960, for instanceusing access categories according to the standardized EDCA medium accessmechanism.

The AP waits for the NDP feedback responses from the polled stations(step 970) until the end of the transmission opportunity (TXOP).

At step 980, the AP analyses the NDP feedback responses or lack ofresponse.

If the NDP feedback packet is sent by a polled station (i.e. one of thestation indicated in the NDP feedback trigger frame), it means that theanswer to the closed-ended question indicated in the “Service Info”field of the NDP feedback trigger frame is positive.

Otherwise, if no NDP feedback packet is sent, it means either that thepolled station has not received the trigger frame or that the polledstation is no more available (battery problem) or that the answer to theclosed-ended question indicated in the “Service Info” field of the NDPfeedback trigger frame is negative.

In practice, this analysis may be performed using a single energydetection mechanism or a standardized decoding process of the 802.11 PHYlayer (503 in FIG. 5 ).

Finally, at step 990, the AP transmits the results to the Applicationlayer (501 in FIG. 5 ) or from the MAC 802.11 layer (504 in FIG. 5 ) inresponse to the request received at step 900.

FIG. 10 illustrates, using a flowchart, steps of a communication methodperformed by a station (non-AP node), according to embodiments of theinvention, when the station receives a NDP feedback trigger frame.

The station waits for reception of a NDP feedback trigger frame at step1000. According to embodiments, when receiving a trigger frame, thestation knows that it is a NDP feedback trigger frame thanks to thevalue of the “Trigger Type” field (620 in FIG. 6 ). The station thusknows that a NDP feedback process is being performed on thecommunication channel.

At step 1010, the station retrieves the “Map Info” field of the NDPfeedback trigger frame.

At step 1020, the station determines whether its own AID matches withone of the AID subfields of the “Map Info” field. If this is not thecase, the process loops back to step 1000 and the station waits toreceive a new NDP feedback trigger frame.

Otherwise, if its AID is indicated in the “Map Info” field, the stationdetermines at step 1030, the position at which it is expected to sendthe NDP feedback response packet. This position is also indicated in the“Map Info” field, as described with reference to FIG. 6 .

At step 1040, the station retrieves the question indicated in the“Question” subfield of the “Service Info” field of the NDP feedbacktrigger frame and determines whether the answer to this question ispositive.

If the response to this question is positive, the station builds (step1050) a NDP feedback packet as described with reference to FIG. 7 andsends it at step 1060 at the position retrieved at step 1030.

Finally, the process loops back to step 1000 and the station waits toreceive a new NDP feedback trigger frame.

Although the present invention has been described hereinabove withreference to specific embodiments, the present invention is not limitedto the specific embodiments, and modifications will be apparent to askilled person in the art which lie within the scope of the presentinvention.

Many further modifications and variations will suggest themselves tothose versed in the art upon making reference to the foregoingillustrative embodiments, which are given by way of example only andwhich are not intended to limit the scope of the invention, that beingdetermined solely by the appended claims. In particular the differentfeatures from different embodiments may be interchanged, whereappropriate.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that different features are recited in mutuallydifferent dependent claims does not indicate that a combination of thesefeatures cannot be advantageously used.

The invention claimed is:
 1. A communication method in a wirelesscommunication network comprising an access point and a plurality ofstations, the method comprising, at a station: receiving a null datapacket, NDP, feedback report poll, NFRP, trigger frame reserving atransmission opportunity on the communication channel and defining tonesets for the stations to transmit NDP feedback responses to the accesspoint; wherein the NFRP trigger frame comprises a first field allowingthe station to identify the NFRP trigger frame as being a NFRP triggerframe dedicated to initiate collection of the NDP feedback responsesfrom stations of the plurality during the reserved transmissionopportunity; and wherein the NFRP trigger frame further comprises asecond field indicating a type of the NDP feedback responses which thestations are allowed to provide, wherein the type of the NDP feedbackresponses indicated by the second field includes at least a typeindicating that resource requests from the stations are being calledfor.
 2. The method according to claim 1, comprising the following steps:determining whether the station is targeted by the received NFRP triggerframe; and if so: building a NDP feedback response to the received NFRPtrigger frame; and sending the NDP feedback response to the access pointin the transmission opportunity reserved by the access point.
 3. Themethod according to claim 1, wherein a NDP feedback response is sent bythe station in a packet with no data payload over tone sets adapted tobe analyzed using a single energy detection mechanism by the accesspoint.
 4. The method according to claim 2, also comprising: identifying,based on the received NFRP trigger frame, a position at which a NDPfeedback response to it should be sent; wherein sending the NDP feedbackresponse to the access point is done at the identified position.
 5. Themethod according to claim 2, also comprising: retrieving, based on thesecond field in the received NFRP trigger frame, a type of NDP feedbackresponses to be collected from the stations; and determining theresponse to the type; wherein the NDP feedback response is built basedon the determined response.
 6. The method according to claim 5, whereinthe type is a closed-ended question.
 7. The method according to claim 1,wherein a NDP feedback response is a packet made only of a PHY preamblewith no data payload.
 8. A communication device station in a wirelesscommunication network comprising an access point and a plurality ofstations, the communication device comprising at least onemicroprocessor configured for carrying out the following step: receivinga null data packet, NDP, feedback report poll, NFRP, trigger framereserving a transmission opportunity on the communication channel anddefining tone sets for the stations to transmit NDP feedback responsesto the access point; wherein the NFRP trigger frame comprises a firstfield allowing the station to identify the NFRP trigger frame as being aNFRP trigger frame dedicated to initiate collection of the NDP feedbackresponses from stations of the plurality during the reservedtransmission opportunity; and wherein the NFRP trigger frame furthercomprises a second field indicating a type of the NDP feedback responseswhich the stations are allowed to provide, wherein the type of the NDPfeedback responses indicated by the second field includes at least atype indicating that resource requests from the stations are beingcalled for.
 9. A dedicated Null Data Packet, NDP, feedback report poll,NFRP, trigger frame designed to be sent by an access point of a wirelesscommunication network comprising a plurality of stations, the NFRPtrigger frame comprising: a first field allowing the stations receivingthe NFRP trigger frame to identify the NFRP trigger frame as being aNFRP trigger frame dedicated to initiate collection of NDP feedbackresponses from stations of the plurality during a transmissionopportunity reserved by the access point; and a second field indicatinga type of the NDP feedback responses to be collected from the stations,wherein the type of the NDP feedback responses indicated by the secondfield includes at least a type indicating that resource requests fromthe stations are being called for.
 10. The NFRP trigger frame accordingto claim 9, wherein the type calls for resource requests from stationsable to receive the NFRP trigger frame.
 11. The NFRP trigger frameaccording to claim 9, wherein the type is about the status of at leastone component of a station able to receive the NFRP trigger frame. 12.The NFRP trigger frame according to claim 9, wherein the type is aclosed-ended question.
 13. The NFRP trigger frame according to claim 9,wherein the NFRP trigger frame comprises information indicating a groupof stations to be polled.
 14. The NFRP trigger frame according to claim9, comprising a third field specifying the position at which a NDPfeedback responsive to the NFRP trigger frame should be sent.